Everyone has heard of the so-called Pacific Garbage Patch. The imagery is compelling: a giant, continent-sized, swirling vortex of plastic lawn chairs and newspapers, red party cups and potato chip bags. The truth is just as troubling, but perhaps less narratively gripping. There actually are millions of small pieces of plastic floating atop some 5000 square kilometers of the Pacific (and elsewhere), but they’re mostly microscopic. It’s estimated that there are about .4 bits of plastic for every cubic meter of surface water.

Floating bits of human waste are not new. The first documented discovery of a seabird who had swallowed a bit of trash may be in an 1838 letter from Jonathan Couch to the Linnean Society in which he describes his investigation into the stomach contents of a Wilson’s storm petrel that had washed up: “On examining the stomach of a stormy petrel Mr. Couch found about half an inch of a common tallow candle, of a size so disproportionate to the bill and gullet of the bird, that it seems wonderful how it could have been able to swallow it.”

Perhaps the first formal scientific study of the ingestion of plastic by seabirds was conducted in the 1960s, which focused on Laysan Albatross. By the 1990s, researchers had identified plastic in the stomachs of more than 35% of the world’s seabird species. Even now, an estimated twenty million new items find their way into the sea each day.

Until now, most studies focused on the amount of plastic visible in the stomach cavities of seabirds. Now, Canadian and Australian researchers have determined the extent to which trace metals from those plastics contaminate seabirds’ tissues. Toxic amounts of trace metals like silver, chromium, cadmium, mercury, and lead could in result in physiological disruptions, infection, and neurological impairments.

To address the question, the researchers turned to a colony of Flesh-footed shearwaters (Puffinus carneipes) on eastern Australia’s Lord Howe Island, where the world’s largest population of the species has been declining for more than twenty years.

Led by Jennifer L. Lavers of Monash University, the team discovered that the birds showed high concentrations of both chromium and silver even as fledglings, and that the concentration level for each was positively correlated with the mass of ingested plastic that they washed out of the birds’ stomachs. In other words, the more plastic they gobbled up, the more concentrated the metals were in their tissues.

Prior research had indicated that if chromium concentration in avian tissues exceeds 2.8 milligrams per gram, it can lead to adverse neurotoxic effects. Three of the nine fledglings for which they were able to detect chromium were far above that threshold, with a range of 3.7 to 6.1 milligrams per gram. While silver is also considered toxic, the researchers acknowledged that “much remains to be understood about how the effects of nanosilver, if any, manifest in birds and other wildlife.”

The “lowest observed adverse effect level” for chromium, combined with data on the typical concentration of the metal on and within plastic, suggests that shearwaters could suffer from chromium toxicity if they ingest less than one one-hundred-thousandth of a gram of plastic per day. That’s an amount equivalent to just three grains of sand. Given that, 89 percent of the Flesh-footed shearwater fledglings assessed in this study could become ill or die due to chromium exposure.

According to Lavers and her colleagues, this is the first research that links the harmful effects of plastic ingestion for seabirds with trace metal exposure, and it helps to explain how plastic impacts survival rates for fledglings.

When it came to more traditional measurements, the news wasn’t any better. The number of birds ingesting plastic increased each year over the four-year study. Nearly two thirds of the fledglings exceeded the amount of plastic ingestion that is considered “acceptable” by international standards. More striking, 16 percent of the fledglings exceeded that threshold after just a single feeding.

The takeaway message is simple. If we can’t stop plastic waste from reaching our shores, the future looks grim for Flesh-footed shearwaters and other seabirds. – Jason G. Goldman | 12 February 2014